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December, 1909 TAE Marine REvIEWw 489 ance for model (A) are shown in Fig. 2, the base representing the position of the midship section with respect to the length, and the ordinates to each curve, the residuary resistance for a _ con- stant speed-length ratio. It will be noticed that at the low speeds the position of the midship section thas little or no influence upon the resistance, but as the speed increases there jis a certain position for each speed where the resistance is a mini- mum. This position travels aft as the speed increases. With the midship section 10 per cent aft or. 10 per cent forward of the middle of the length the resist- ance shows a marked increase at the higher speeds. The results for Model B are shown in the same manner in Fig. 3. In general the curves follow in the same linés as those for Model A. In this case, however, as the model is of somewhat fuller form, the minimum occurs at a slightly different place and the ef- fect of the position of the midship section is noticeable at a smaller speed-length ratio. In both models, when the mid- ship section was placed at 10 per cent of the length aft of the cen- ter the flow around the after body seemed somewhat disturbed. This was doubtless due to the hollow form caused by the closing up of the sections, and the performance in this particular case could doubtless be improved by filling out the after body at the stern and easing the form immediately aft of the midship section. Such modifications, however, would de- stroy the main object of the above investigations, which show the effect of the position of the midship section only, everything else remaining constant. In reading the paper Prof. Sadler said in explanation: I would like to call attention to one error which un- fortunately was discovered after these plates were made. The speed wave ratio of 0.9 for the midship section, 10 per cent forward of the middle, the ordinate should be about 3.6, in- stead of 2.6. This curve for 0.9 speed | | | | | * | ¥ 4 2 Ad Mate B Pig. 4A, length ratio should rise a little more rapidly on its right hand side. Location of Center of Buoyancy. DD... W.: Taylors: (1. weuld< like to say one word in expression of my appreciation of Prof. Sadler's paper. It seems to be it brings out one or two facts which are likely to be of very great practical value and inter- est. There is a general impression among the people who have worked on model tanks for a number of years, I think in England more par- ticularly, that it is desirable to place Model. _--_--- the center of buoyancy of the ship a little abaft of the center of length. Some naval architects do not agree with this theory, but I think that the tank people are nearly all of the opinion that the center of buoyancy should be slightly abaft of the center of length. Prof. Sadler's experiments certainly confirm that point of view as far as that goes, because by shift- ing the midship section he shifted the center of buoyancy. "As @ part of our regular practice, at the model basin, we test models on an even keel, by the head and by the stern, and it A. | 10% 5% : 5% 10% Att 3 Forward t ka Position of Midship Section & FETC.